1. Field of the Invention
The present disclosure relates to the field of production and purification of hydrofluoroolefin compounds. The present disclosure further relates to processes utilizing azeotrope compositions for separation of hydrofluoroolefins from hydrofluorocarbons and hydrogen fluoride.
2. Description of Related Art
Chlorine-containing compounds such as chlorofluorocarbons (CFCs) are considered to be detrimental to the Earth's ozone layer. Many of the hydrofluorocarbons (HFCs), used to replace CFCs, have been found to contribute to global warming. Therefore, there is a need to identify new compounds that do not damage the environment, but also possess the properties necessary to function as refrigerants, solvents, cleaning agents, foam blowing agents, aerosol propellants, heat transfer media, dielectrics, fire extinguishing agents, sterilants and power cycle working fluids. Fluorinated olefins, especially those containing one or more hydrogens in the molecule (referred to herein as hydrofluoroolefins) are being considered for use in some of these applications such as in refrigeration as well as in processes to make fluoropolymers.
1,1,3,3,3-Pentafluoropropene is a useful cure-site monomer in polymerizations to form fluoroelastomers. U.S. Pat. Nos. 6,703,533, 6,548,720, 6,476,281, 6,369,284, 6,093,859, and 6,031,141, as well as published Japanese patent applications JP 09095459 and JP 09067281, and WIPO publication WO 2004018093, disclose processes wherein 1,1,1,3,3,3-hexafluoropropane is heated at temperatures below 500° C. in the presence of catalyst to form 1,1,3,3,3-pentafluoropropene. These low-temperature catalytic routes are chosen because of the well-known tendency for fluorocarbons to fragment at higher temperatures, e.g., above 500° C. This is made clear in Chemistry of Organic Fluorine Compounds, by Milos Hudlicky, 2nd Revised Edition, Ellis Horwood PTR Prentice Hall [1992] p. 515: “Polyfluoroparaffins and especially fluorocarbons and other perfluoro derivates show remarkable heat stability. They usually do not decompose at temperatures below 300° C. Intentional decomposition, however, carried out at temperatures of 500-800° C., causes all possible splits in their molecules and produces complex mixtures which are difficult to separate.”
U.S. Patent Application Publication 2002/0032356 discloses a process for producing the perfluorinated monomers tetrafluoroethylene and hexafluoropropylene in a gold-lined pyrolysis reactor.
The catalytic process has disadvantages, including catalyst preparation, start-up using fresh catalyst, catalyst deactivation, potential for plugging of catalyst-packed reactors with polymeric by-products, catalyst disposal or reactivation, and long reaction times that impose a space/time/yield reactor penalty. It would be desirable to be able to produce 1,1,3,3,3-pentafluoropropene from 1,1,1,3,3,3-hexafluoropropane in high yield by a non-catalytic process.